Within different technical fields, e.g. in the manufacture of collection pouches for receiving drainage from an artificial abdominal opening, a need exists for forming a marginally reinforced hole in a thin thermoplastic sheet material. For this purpose it has been suggested to weld a prefabricated ring or eyelet to the sheet material to surround the hole which may be formed by a stamping or cutting operation either before or subsequent to the welding operation or possibly simultaneously therewith.
In the first case the accurate aligning of the ring with the pre-stamped hole is of vital importance as, otherwise, an edge portion of the sheet material may protrude inwardly from the inner periphery of the ring so as to form a rather hard flap or fin that will cause much nuisance to the user of a pouch of the type referred to in the foregoing. Even when much care is taken, the perfect aligning of the ring or eyelet relative to the edge of the hole may cause great trouble due to the fact that the sheet material is normally rather thin and elastic.
It may be possible to at least substantially eliminate the disagreeable fin by performing the stamping operation subsequent to or at the same time as the welding operation but, then, a more complicated machinery must be used and in the latter case the quality and strength of the welding seam may further be detrimentally influenced by the strains to which the sheet material is subjected due to the operation of the stamping tool.
The embarrassing flap or fin may be completely eliminated when the sheet material inside the ring is cut away, during or after the welding operation, by means of a rotary knife following the inner periphery of the ring. However, a rather complicated mechanism is then necessary, and there is a substantial risk that the operation of this mechanism will be disturbed by the heat influence from the welding zone, especially then the welding and cutting operations are performed at the same time in order to minimize the total processing time.